Personal aircraft

ABSTRACT

A safe, quiet, easy to control, efficient, and compact aircraft configuration is enabled through the combination of multiple vertical lift rotors, tandem wings, and forward thrust propellers. The vertical lift rotors, in combination with a front and rear wing, permits a balancing of the center of lift with the center of gravity for both vertical and horizontal flight. This wing and multiple rotor system has the ability to tolerate a relatively large variation of the payload weight for hover, transition, or cruise flight while also providing vertical thrust redundancy. The propulsion system uses multiple lift rotors and forward thrust propellers of a small enough size to be shielded from potential blade strike and provide increased perceived and real safety to the passengers. Using multiple independent rotors provides redundancy and the elimination of single point failure modes that can make the vehicle non-operable in flight.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/931,954, filed Jun. 30, 2013 which is a continuation of U.S.application Ser. No. 13/553,438, now U.S. Pat. No. 8,485,464, filed onJul. 19, 2012, which claims the benefit of provisional application No.61/509,530, filed on Jul. 19, 2011. All applications are incorporated byreference herein in their entirety.

BACKGROUND Field of the Invention

This disclosure relates generally to a personal aircraft configured toprovide safe operations while achieving robust control. In particular,the described embodiments include an aircraft with vertical takeoff andlanding capability, and that provides vertical and horizontal thrust ina controlled fashion for hover, transition and cruise flight.

Description of Related Art

Taking off and landing vertically, instead of using a runway to developsufficient velocity on the ground for wings to provide adequate lift,requires an aircraft to provide both vertical and forward thrust. Thrustproduced in the vertical direction provides lift to the vehicle; thrustproduced horizontally provides forward movement. A vertical takeoff andlanding (VTOL) aircraft can produce both vertical and horizontal thrust,and is able to control these forces in a balanced fashion.

The rotary wing aircraft, or helicopter, is one common type of VTOLaircraft. Helicopters have large rotors that provide both vertical andhorizontal thrust. For the rotors to perform this dual function across arange of airspeeds, the rotors are typically quite complex. Depending onthe vehicle flight condition, the rotor blades must be at differentorientation angles around the 360 degrees of azimuth rotation to providethe needed thrust. Therefore, rotors have both collective and cyclicvariation of the blade orientation angle. Collective varies the angle ofeach blade equally, independent of the 360-degree rotation azimuthangle. Cyclic varies the blade angle of attack as a function of the360-degree rotation azimuth angle. Cyclic control allows the rotor to betilted in various directions and therefore direct the thrust of therotor forwards, backwards, left or right. This direction providescontrol forces to move the helicopter in the horizontal plane andrespond to disturbances such as wind gusts.

Helicopter rotors are large and unprotected from hitting nearbyobstacles. Additionally, they utilize mechanically complex systems tocontrol both the collective and cyclic blade angles. Such rotors aremechanically complex and require maintenance. The rotors generallyrotate at a low speed; this results in heavy transmissions between therotor and motor. The transmissions, or gearboxes, decrease the vehiclepayload potential, as well as vehicle safety. Because of the mechanicalcomplexity across the entire vehicle system, many parts are singlepoints of failure. Because of this lack of redundancy, frequentinspections and maintenance are required to keep the vehicle safe.

SUMMARY

The described embodiments provide a personal aircraft with aconfiguration that is safe, quiet, and efficient, as well as easy tocontrol, highly compact, and able to accomplish vertical takeoff andlanding with transition to and from forward flight. In one embodiment,the aircraft configuration includes multiple rotors oriented to providevertical thrust for lift and control during takeoff, transition to andfrom forward flight, and landing. The rotors are attached to theairframe in fixed, non-planar orientations. The orientations of rotorsprovide lateral and, in some embodiments, fore and aft control ofaircraft without requiring a change of attitude, and minimizedisturbances to the flow when the aircraft is cruising. In variousembodiments, the rotors have forward, backwards, left, and rightorientations, and are located longitudinally along the port andstarboard sides of the fuselage, with two or more rotors located on eachside.

The fuselage carries a variable-weight payload. The aircraft has tandemwings at the front and rear of the vehicle. The wings provide lift andcontrol during cruise, and one or more propellers provide forwardthrust. The combination of vertical lift rotors and front and reartandem wings bound the rotors, permitting movement in the aircraft'scenter of gravity while still enabling the vehicle to maintain verticaland horizontal flight control. The forward and rear wings are alsolocated to provide a boundary to avoid foreign object damage (FOD) tothe lift rotors. The control surfaces, which include elevator andailerons, are usable to compensate for changes in CG of the aircraftduring flight by adjusting the center of lift, in addition to changingangle of attack and attitude. The vertical lift rotors are arrangedaround the CG, and the thrust of each rotor is adjustable, which permitsthe relocation of the center of lift in vertical flight if the CGshifts.

Due to the multiple number and independence of the vertical lift rotors,the vertical thrust is redundant and thrust and control remain availableeven with the failure of any single rotor. Since there are multiplevertical rotors that provide large control forces, the rotors aresmaller, with faster response rates for operation even in gusty windconditions. In one embodiment, a separate electric motor and controllerpowers each vertical lift rotor, in order to provide lift systemredundancy from failure of one or more lifting rotors. In otherembodiments, the vertical thrust rotors are embedded in ducts thatconceal them and provide increased lift. Other embodiments arerelatively open with protective shrouding to act as guards to preventcontact with other objects and prevent FOD to the rotors. The protectiveshielding in combination with in-line vertical lift rotors provide lowcruise drag for efficient flight. Low tip speed vertical lift rotors areused in various embodiments to produce low community noise levels duringtakeoff, transition, and landing. Embodiments with a low front wing andhigh rear wing with winglets provide high aerodynamic efficiency whilealso providing yaw stability for the aircraft. In some embodiments, thewings fold to provide a compact vehicle footprint when in hover or whileon the ground. Some embodiments of the wing have control surfaces onlyon the inner part of the wing fold so that no articulating controllinkages are required. Since the lift rotors that are used for verticallift are separate from the forward thrust propellers, each is optimizedfor its specific operating conditions. Such a vehicle can be used foreither piloted or unpiloted embodiments across a range of occupant sizesor payloads.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a personal aircraft vehicle in accordance withone embodiment.

FIG. 2 illustrates a second view of a personal aircraft vehicle inaccordance with one embodiment.

FIG. 3 illustrates a front view of a personal aircraft vehicle inaccordance with one embodiment.

FIG. 4 illustrates a view of the left side of a personal aircraftvehicle in accordance with one embodiment.

FIG. 5 is a block diagram illustrating a flight computer in accordancewith one embodiment.

FIG. 6 is a flowchart illustrating a method for transitioning fromvertical takeoff to forward flight in accordance with one embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a personal aircraft 100 in accordance with oneembodiment. Aircraft 100 includes vertical lift rotor assemblies 101 aand 101 b (generally, 101) with fixed orientations; forward flightpropellers 103; a forward wing 104; a rear wing 105 having winglets 106a and 106 b (generally, 106); fences 110 a and 110 b (generally 110), acockpit area 112 and a fuselage 107. Fuselage 107 also includes landinggear, a flight computer and power source (not shown), each of which isdescribed further below. FIG. 2 illustrates a second view of personalaircraft 100, including propulsion booms 114, port-side main landinggear 202 and forward landing gear 204. FIG. 3 illustrates a front viewof personal aircraft 100, in which port landing gear 202 a, starboardlanding gear 202 b and nose gear 204 are visible. FIG. 4 illustrates aview of the left (port) side of aircraft 100 in accordance with oneembodiment.

In various embodiments, aircraft 100 is sized to accommodate a singlepilot and personal cargo. For example, in various embodiments the lengthof the aircraft from nose to its aft-most surface is between 15 and 20feet, and its wingspan is between 15 and 20 feet. In alternativeembodiments, the aircraft may be longer or shorter, wider or narrower,as will be appreciated by those of skill in the art, without departingfrom the principles described here.

Aircraft 100 is constructed in various embodiments primarily of acomposite material. Fuselage 107 and wings 104, 105 are made from carbonfiber composite material. In alternative embodiments, the wings may havemetal fittings and ribs attached to the inside and outside of a carbonfiber composite wing skin. In some embodiments the wing skins maycomprise composite materials made of carbon fiber combined with othercomposite materials such as Kevlar. In other alternative embodiments,the fuselage may comprise a metal truss made from steel or aluminum witha composite skin that covers the truss. The composite fuselage skin inthis embodiment may be made of carbon fiber, Kevlar, or other compositematerials as understood by those of skill in the art. The cockpitwindows in one embodiment are polycarbonate, though other lightweightclear plastics may also be used. Fences 110 are made from a Kevlar andcarbon fiber composite.

Rotor assemblies 101 include rotors that in one embodiment have a 16inch radius, and are made from carbon fiber composite material, and inan alternative embodiment from carbon fiber composite blades attached toan aluminum hub. In other embodiments, rotors are made from wood bladesattached to an aluminum hub, or wood blades attached to a carbon fibercomposite hub. The rotors may be a single piece that bolts onto themotor assembly. Rotor assemblies 101 are described further below.

Aircraft 100 includes a forward wing 104 and an aft wing 105. Tomaintain minimal length and width and have the CG in the center of therotor system, the forward and aft wings are similar in span. The aftwing is swept back and has winglets 106 at its ends. The wingletsprovide lateral stability and decrease the drag due to lift on the aftwing. Sweeping the wing back improves the pitch stability of theaircraft and increases the benefits of the winglets on lateralstability. In some embodiments the aft wing can fold, and thus maintainthe same overall vehicle length as an aircraft with an unswept aft wing.Additionally, the sweep of the aft wing provides more space for therotors to fit into. Forward wing 104 is also attached to fuselage 107 ata point substantially lower than is aft wing 105 in various embodiments.A non-planar wing lifting system enables the wings to develop efficientlift during cruise flight. In one embodiment, the vertical separationbetween the two wings is chosen to be as large as possible, given theconstraint of attaching to the fuselage. By maximizing the wing verticalseparation, the negative aerodynamic interaction between the front wingand the rear wing is reduced. Thus, the drag due to lift of the vehicleis significantly decreased, for example by 15-20% compared to a singlein-plane wing lifting system.

The winglets 106 are located at the tip of rear wing 105 to providedecreased drag due to lift on the rear wing, as well as yaw ordirectional stability and control. The particular winglet shape isestablished for adequate stability, as will be understood by thoseskilled in the art. In some embodiments, as illustrated in FIG. 3, thewinglets extend downward and provide improved controllability byreducing the coupling between the sideslip angle of the aircraft and theyawing moment that the airflow produces on the aircraft.

In one embodiment, the tandem wing system has joints where the wingtipson each wing fold, allowing aircraft 100 to fit in a constrained space.For example, in one embodiment folding the wings enables the aircraft100 to be stored an 8′ by 7′ by 16′ space, or the space provided by atypical single car garage. In one embodiment the rear wing 105 has adihedral angle of 8.4 degrees. In other embodiments the dihedral rangesbetween −10 and 10 degrees.

Vertical lift rotor assemblies 101 are mounted on each side of aircraft100. In one embodiment, a propulsion boom 114 (FIG. 2) is secured toeach side of the fuselage 107. In this embodiment, forward flightpropellers 103 are attached to the rear end of the booms 114, and thevertical lift rotor assemblies 101 are installed on top of the booms114. Propulsion booms 114 are attached to the fuselage 107 with struts116. The struts 116 are positioned so that the downwash from the rotorsdoes not impinge on the struts. In some embodiments there are threestruts connecting each boom to the fuselage. In alternative embodimentsthere are one or two struts connecting each boom to the fuselage. Inother embodiments the struts may be swept forward, aft, up, or down toimprove the attachment of the booms to the fuselage. For example, in analternative embodiment a vertically oriented support structure providesincreased bending stiffness from the vertical lift rotor loads duringhover.

Each vertical lift rotor assembly 101 includes a rotor and a motor. Therotor may comprise blades attached to a hub, or may be manufactured as asingle piece with an integral hub. The hub provides a central structureto which the blades connect, and in some embodiments is made in a shapethat envelops the motor. The motor includes a rotating part and astationary part. In one embodiment the rotating part is concentric tothe stationary part, known as a radial flux motor. In this embodimentthe stationary part may form the outer ring of the motor, known as aninrunner motor, or the stationary part may form the inner ring of themotor, known as an outrunner motor. In other embodiments the rotatingand stationary parts are flat and arranged in opposition to each other,known as an axial flux motor. In some embodiments the motor parts arelow-profile so that the entire motor fits within the hub of the rotor,presenting lower resistance to the air flow when flying forward. Therotor is attached to the rotating part of the motor. The stationary partof the motor is attached to the propulsion boom 114. In some embodimentsthe motor is a permanent magnet motor and is controlled by an electronicmotor controller. The electronic motor controller sends electricalcurrents to the motor in a precise sequence to allow the rotor to turnat a desired speed or with a desired torque.

As noted, aircraft 100 includes multiple rotor assemblies 101 per side.The vertical lift rotors generate thrust that is independent of thethrust generated by the forward flight propellers 103 during horizontalcruise. The vertical lift rotors provide enough thrust to lift theaircraft off the ground and maintain control. In one embodiment, eachrotor generates more, e.g., 40% more, thrust than is needed to hover, tomaintain control in all portions of the flight envelope. The rotors areoptimized by selecting the diameter, blade chord, and blade incidencedistributions to provide the needed thrust with minimum consumed powerat hover and low speed flight conditions. In various embodiments, halfof the rotors rotate in one direction, and the other half rotate in theopposite direction to balance the reaction torque on the aircraft. Insome embodiments, rotors directly across from each other on the port andstarboard sides of the aircraft have opposite directions of rotation. Inother embodiments the rotors directly across from each other have thesame direction of rotation. In some embodiments, the rotors may beindividually tuned to account for different interactions between therotors, or between the airframe and the rotors. In such embodiments thetuning includes adjusting the incidence or chord distributions on theblades to account for favorable or adverse interactions and achieve thenecessary performance from the rotor. In the embodiment illustrated inFIG. 1, four vertical lift rotor assemblies 101 per side are shown. Inalternative embodiments more or fewer vertical lift rotors provide thevertical lift and control. When at least two rotors per side arepresent, the ability to produce a vertical force with equilibrium aboutthe center of gravity is retained even when one rotor fails. This isachieved by decreasing the thrust on the opposite quadrant to the failedrotor. When three rotors per side are present, control about all threeaxes, or directions of flight, is available. As the number of rotors perside increases, the loss of any one rotor results in a decreasingoverall loss of vertical thrust. However, with each extra pair of rotorsthere is increasing complexity and probability that a failure wouldresult, as well as increased cost and weight.

In one embodiment, two vertical lift rotor assemblies 101 per side arelocated in front of the CG and two are located behind the CG. In thismanner, the center of lift of the rotors in hover is co-located with thecenter of gravity of the aircraft 100. This arrangement permits avariation of longitudinal or lateral positioning of the payload in thefuselage 107. Flight computer 500 modifies the thrust produced by eachvertical lift rotor independently, providing a balanced vertical liftor, alternatively, unbalanced lift to provide control.

In some embodiments, the rotor orientation provides lateral andlongitudinal control of the aircraft without requiring a change ofattitude. Because rotor assemblies 101 are each mounted to cant outward,inward, forward, or back, a proper combination of rotor thrusts resultsin a net force in the horizontal plane, as well as the needed verticallift force. This is helpful when maneuvering near the ground, forexample. In addition, in the case of a rotor failure in which a bladebecomes damaged or separated, the different cant angles make it lesslikely that another rotor will be damaged, thus making the design morefailure tolerant. The orientations are also chosen to minimizedisturbances to the flow when the aircraft is cruising. In someembodiments, the orientation of the rotors is varied forward, backward,left, and right, enabling the aircraft to maneuver in any directionwithout changing attitude. In other embodiments, the orientation isvaried only left and right, minimizing the disturbance to the flowduring cruise, but meaning that the aircraft can only maneuverside-to-side, not forward and backward, without changing attitude. Inone embodiment with four rotors per side, the rotors are oriented, fromfront to back, 10 degrees out, 10 degrees in, 10 degrees in, and 10degrees out.

Forward flight propellers 103 provide the thrust for transition toforward flight, climb, descent, and cruise. In one embodiment two ormore forward thrust propellers 103 are mounted along the span of therear wing 105. In alternative embodiments, a single forward thrustpropeller is mounted on the aft portion of the fuselage 107 at thecenter of the span. In other embodiments, one or more propellers aremounted to the front of the wings or propulsion booms as tractorpropellers. The propellers can be rotated in opposite directions so thatthe torque required to turn them does not produce a net torque on theairplane. Also, the thrust of the two propellers can be varieddifferentially to provide a yaw control moment. Positioning on the wingresults in less inflow disturbance to the propellers. Use of a singlepropeller on the fuselage permits fewer components and less weight, butwith a different-sized motor and with the inflow including disturbancesfrom the fuselage. In one embodiment, the forward propellers arefixed-pitch. The chord and incidence distributions are optimized toprovide adequate thrust for acceleration and climbing both when thevehicle is moving slowly and supported in the air by the thrust of therotors and when the aircraft is moving quickly and is fully supported bythe lift of the wings. Additionally, the chord and incidencedistributions are selected to provide efficient thrust at the cruisingspeed of the aircraft. In other embodiments the forward propellersutilize a variable pitch mechanism which allows the incidence of eachblade to be adjusted depending on the flight condition.

The vertical lift rotors and the forward propellers are driven byelectric motors that are powered by a power system. In one embodimentthe power system includes a battery that is attached to one motorcontroller for each motor. In one embodiment the battery comprises oneor more modules located within the fuselage of the aircraft. In otherembodiments the battery modules are located in the propulsion booms. Thebattery provides a DC voltage and current that the motor controllersturn into the AC signals that make the motors spin. In some embodimentsthe battery comprises lithium polymer cells connected together inparallel and in series to generate the needed voltage and current.Alternatively, cells of other chemistry may be used. In one embodimentthe cells are connected into 93 cell series strings, and 6 of thesestrings are connected in parallel. In other embodiments, the cells areconnected with more or fewer cells in series and more or fewer cells inparallel. In alternative embodiments, the rotors and propellers arepowered by a power system that includes a hybrid-electric system with asmall hydrocarbon-based fuel engine and a smaller battery. Thehydrocarbon engine provides extended range in forward flight and canrecharge the battery system.

The vertical lift rotor assemblies 101 in various embodiments areprotected by protective fences 110 to avoid accidental blade strikes. Insome embodiments the protective fence is designed to maximize the thrustof all the rotors near the fence by providing incremental lift. In thisembodiment the fence 110 is shaped so that the flow over the fenceinduced by the rotor system 101 creates an upward force on the fence110. This is accomplished by selecting a cross sectional shape and anglewith respect to vertical of the fence that generates the upward force.In some embodiments the fence is designed to reduce the apparent noiseof the rotor system by shielding bystanders from the noise of therotors. In these embodiments, the fences are either filled with aconventional sound absorbing material, or are coated with a conventionalsounds adsorbing material. In some embodiments, aircraft 100 does notinclude fences 110.

As noted, the use of multiple independently controlled rotors provides aredundant lift system. For example, a system that includes six or morerotors permits hover and vertical ascent/descent with safe operationwithout forward airspeed, even if one or several individual componentsfail.

FIG. 5 is a block diagram of a flight computer 500 in accordance withone embodiment. Flight computer 500 is located on board aircraft 100,typically within the fuselage 107. Flight computer 500 includes a rotorcontrol module 502, propeller control module 504, position sensorinterface 506, and a database 508. Position sensor interface 506 iscommunicatively coupled to the aircraft's instruments and receivessensor data in one embodiment that includes the aircraft's position,altitude, attitude and velocity. Rotor control module 502 receives datafrom position sensor interface 506 and from control inputs in thecockpit and determines how much thrust is required from each of thevertical lift rotors 101 to achieve the commanded response. Rotorcontrol module 502 commands each rotor assembly 101 independently toproduce the determined required thrust. In the event of a rotor failure,rotor control module 502 adjusts the thrust requirements to compensatefor the lost rotor. Propeller control module 504 receives data fromposition sensor interface 506 and from control inputs in the cockpit,determines how much forward thrust is required from each of thepropellers 103, and commands the propellers to produce the requiredthrust. Database 508 includes programmed trajectories for ascent anddescent to be used during transition, and may also include additionalfeatures used for navigation and control of aircraft 100 as will beappreciated by those of skill in the art. Flight computer 500 alsoincludes other components and modules to perform navigation and flightoperations and which are known to those of skill in the art, but notgermane to this description.

FIG. 6 illustrates a method for transitioning from vertical to forwardflight in accordance with one embodiment. To begin, rotor control module502 of flight computer 500 applies 602 power to the rotors. In oneembodiment, equal power is applied to each of the rotors during thisinitial phase of takeoff. In alternative embodiments different power isapplied to each rotor during the initial phase of takeoff to facilitatetaking off from a slope, or in a crosswind. Position sensor interface506 receives 604 attitude and altitude data from aircraft instruments.Once a minimum altitude, e.g., 200 feet above ground level, has beenreached 606, propeller control module 504 activates 608 the forwardpropellers and in some embodiments activates their control input insidethe cockpit. This prevents the aircraft from being accelerated forwardunder power at altitudes where ground obstructions may present a safetyhazard. In an alternative embodiment, no minimum altitude is requiredfor powered forward propulsion. In other embodiments, the minimumaltitude is adjustable and/or overrideable. For example, tall trees maydemand a higher initial ascent before beginning acceleration.

In some embodiments, the pilot programs an initial altitude into flightcomputer 500. Alternatively, the pilot uses flight control input toindicate that a higher altitude is desired. If 610 additional altitudeis required, position sensor interface 502 determines 612 the aircraft'sattitude and velocity and rotor control module 502 adjusts 614 power tothe rotors individually as needed to maintain vertical thrust and alevel orientation.

Once 610 the aircraft 100 has attained the desired initial altitude,position sensor interface 506 determines 616 whether the forwardvelocity of the aircraft is sufficiently large to generate lift, i.e.,whether the aircraft's speed is greater than its stall speed. If not,flight computer 500 determines 618 how much lift is required from therotors, and applies 620 the required power. In one embodiment, theamount of lift required is the amount required to maintain theaircraft's altitude in view of the lift generated by the airfoils. Asthe speed increases, the wings develop lift and the thrust required ofthe vertical lift rotors is decreased. In one embodiment, the thrustfrom the rotors is adjusted to maintain during the transition an optimaltrajectory and reject any disturbances due to interactions orenvironmental effects such as gusts. In one embodiment, the optimaltrajectory is determined prior to flight and stored by flight computer500 in database 508. Flight computer 500 continues to determine 622 theaircraft's attitude, altitude and velocity and adjust rotor power untila desired speed is reached or a minimum level of lift is being generatedby the airfoils. Once 616 the speed is greater than the stall speed,i.e., high enough that the wings can support the entire weight of theaircraft, or in an alternative embodiment a different minimum speed isreached, the vertical lift rotors are completely deactivated 624.

To transition the aircraft 100 from forward to vertical flight,propeller control module 504 reduces the thrust of the forwardpropellers 103 to reduce speed. As the speed of the aircraft 100 isreduced, rotor control module 502 automatically commands the rotors tobegin generating vertical lift. The thrust required of the vertical liftrotors increases as the lift on the wings decreases. The thrust from therotors is adjusted by rotor control module 502 in response to readingsfrom position sensor interface 506 to maintain during the transition anoptimal trajectory determined by the flight computer, e.g., based on atrajectory stored in database 508, and reject any disturbances due tointeractions or environmental effects such as gusts. Eventually theforward speed is zero or approaching zero and the vertical lift rotorsprovide all the lift. The vehicle then descends to the ground either viaa descent command from the pilot, or by flight computer 500automatically reducing power to the individual rotors to maintain adesired descent rate and a level orientation.

As noted, wing 104 and 105 fold in some embodiments. Some embodimentshave a wing fold that is positioned at a location where the loads aresmall, outboard of 50% of the span, for example, to permit a lighterweight hinge. In other embodiments, the forward wing does not fold. Inother embodiments, the wings fold so the aircraft can fit into an 8′wide space, such as a typical single car garage. Alternative embodimentsalso include folding the forward wing in other ways, such as in ascissor motion underneath the fuselage or along the side of thefuselage. This scissor folding is accomplished through pivot and pin atthe center of the front wing that permits a rotation backwards aboutthat center pivot point. This embodiment permits wing articulation abouta single point to reduce weight at a location where the wing structuraldepth is largest, as well as enabling the front wing to be foldedcompletely away to the side of the vehicle by an electro mechanicalactuator to promote better pilot visibility while in hover or on theground. In an embodiment including a scissor-fold front wing, thelanding gear includes a single front wheel 204 with two main rearlanding gear wheels 202.

In one embodiment, aircraft 100 is capable of taking off and landingwith the front and rear wings folded. Taking off and landing with thewings folded in vertical flight decreases the gust response of thevehicle due to unsteady wind conditions through decreased wing liftperformance and shorter wing spans. Since the wing lift is not requiredin hover flight, but only in forward flight, is it possible to wait tounfold the wings until sufficient altitude is achieved away from ground.Avoiding ground wing unfolding is advantageous for some operations wherethe ground takeoff and landing space available and wind conditions arenot favorable. An electromechanical actuator provides the actuationforce to unfold the wing before commencing forward flight.

In one embodiment, control surfaces are located on the inner portion ofthe front wing fold 301 and rear wing fold 302 to permit folding withoutcontrol lines required outboard of the folding hinge mechanism toprovide less mechanical complexity through fewer moving parts. Thecontrol surfaces provide pitch, roll, and yaw control during forwardflight aerodynamically so that the vertical lift rotors are not requiredfor control except at low or zero forward speed. Other embodiments thatrequire greater forward flight control responsiveness also have controlsurfaces outboard of the wing fold mechanism. Other embodiments onlyhave control surfaces on the outboard section of the wing.

Landing gear 202, 204 is provided with wheels to permit the aircraft tomove while on the ground. One forward 204 and two rear 202 main landinggear provide lower drag and less lift interference on the front wing. Inother embodiments the landing gear is a skid and has no wheels, sincethe aircraft is capable of takeoff and landing without forward movement.Alternative embodiments include two forward and one rear main landinggear to permit the front landing gear to be widely separated for groundstability. In some embodiments, some or all of the wheels are fittedwith electric motors that allow the wheels to be driven. Such motorsallow the vehicle to be self-propelled while on the ground.

In addition to the embodiments specifically described above, those ofskill in the art will appreciate that the invention may additionally bepracticed in other embodiments. For example, in an alternativeembodiment, aircraft 100 is designed to accommodate two or moreoccupants. In such an embodiment, the wingspan is larger, the rotorshave a larger diameter, and the fuselage 107 is wider. In an alternativeembodiment, aircraft 100 is an unmanned vehicle that is capable offlight without a pilot or passengers. Embodiments without passengershave additional control systems that provide directional control inputsin place of a pilot, either through a ground link or through apredetermined flight path trajectory.

Although this description has been provided in the context of specificembodiments, those of skill in the art will appreciate that manyalternative embodiments may be inferred from the teaching provided.Furthermore, within this written description, the particular naming ofthe components, capitalization of terms, the attributes, datastructures, or any other structural or programming aspect is notmandatory or significant unless otherwise noted, and the mechanisms thatimplement the described invention or its features may have differentnames, formats, or protocols. Further, some aspects of the systemincluding components of the flight computer 500 may be implemented via acombination of hardware and software or entirely in hardware elements.Also, the particular division of functionality between the varioussystem components described here is not mandatory; functions performedby a single module or system component may instead be performed bymultiple components, and functions performed by multiple components mayinstead be performed by a single component. Likewise, the order in whichmethod steps are performed is not mandatory unless otherwise noted orlogically required.

Unless otherwise indicated, discussions utilizing terms such as“selecting” or “computing” or “determining” or the like refer to theaction and processes of a computer system, or similar electroniccomputing device, that manipulates and transforms data represented asphysical (electronic) quantities within the computer system memories orregisters or other such information storage, transmission or displaydevices.

Electronic components of the described embodiments may be speciallyconstructed for the required purposes, or may comprise one or moregeneral-purpose computers selectively activated or reconfigured by acomputer program stored in the computer. Such a computer program may bestored in a computer readable storage medium, such as, but is notlimited to, any type of disk including floppy disks, optical disks,DVDs, CD-ROMs, magnetic-optical disks, read-only memories (ROMs), randomaccess memories (RAMs), EPROMs, EEPROMs, magnetic or optical cards,application specific integrated circuits (ASICs), or any type of mediasuitable for storing electronic instructions, and each coupled to acomputer system bus.

Finally, it should be noted that the language used in the specificationhas been principally selected for readability and instructionalpurposes, and may not have been selected to delineate or circumscribethe inventive subject matter. Accordingly, the disclosure is intended tobe illustrative, but not limiting, of the scope of the invention.

What is claimed is:
 1. An aircraft comprising: a fuselage; a wingcoupled to the fuselage; a first plurality of lift rotors located aft ofa center of gravity of the aircraft, the first plurality of lift rotorscoupled to the fuselage, at least one of the first plurality of liftrotors having a first cant and at least one of the first plurality oflift rotors having a second cant, the second cant having an angledifferent from the first cant; a second plurality of lift rotors locatedforward of the center of gravity, the second plurality of lift rotorscoupled to the fuselage, at least one of the second plurality of liftrotors having a third cant and at least one of the second plurality oflift rotors having a fourth cant, the fourth cant having an angledifferent from the third cant, wherein the fourth cant has an angledifferent from the first cant and the second cant, wherein the firstplurality of lift rotors and the second plurality of lift rotors arecoupled to the fuselage via one or more rotor booms; a propeller coupledto the fuselage for providing forward thrust; and a flight computer,coupled to the fuselage, and configured to independently control anamount of thrust provided by each of the first plurality of lift rotorsand each of the second plurality of lift rotors according to adifference between a current orientation of the aircraft and a desiredorientation of the aircraft.
 2. The aircraft of claim 1, wherein thefirst plurality of lift rotors includes at least 6 rotors and the secondplurality of lift rotors includes at least 6 rotors.
 3. The aircraft ofclaim 1, wherein the flight computer is further adapted to adjust theamount of thrust provided by each of the first plurality of lift rotorsand each of the second plurality of lift rotors to compensate for arotor failure.
 4. The aircraft of claim 1, wherein the flight computerfurther comprises: a position sensor interface, adapted to receivesensor data that indicates one or more of a position, an altitude, anattitude and a velocity of the aircraft; and a rotor control module,coupled to the position sensor interface, adapted to determine theamount of thrust required from each of the first plurality of liftrotors and each of the second plurality of lift rotors to achieve thedesired orientation and to command independently each of the firstplurality of lift rotors or the each of the second plurality of liftrotors to produce the determined required thrust.
 5. The aircraft ofclaim 4, wherein the flight computer further comprises: a propellercontrol module coupled to the position sensor interface, adapted todetermine an amount of forward thrust required from the propeller and tocommand the propeller to produce the required thrust.
 6. The aircraft ofclaim 1, wherein at least one of the first plurality of lift rotors islocated on a starboard side of the fuselage and at least one of thefirst plurality of lift rotors is located on a port side of thefuselage.
 7. The aircraft of claim 1, wherein at least one of the secondplurality of lift rotors is located on a starboard side of the fuselageand at least one of the second plurality of lift rotors is located on aport side of the fuselage.
 8. The aircraft of claim 1, furthercomprising an aft wing coupled to the fuselage.
 9. The aircraft of claim8, wherein the aft wing is located aft of the center of gravity.
 10. Theaircraft of claim 1, wherein each rotor in the first plurality of liftrotors and the second plurality of lift rotors is a rotor assemblyincluding a rotor and a motor, wherein the rotor includes a plurality ofblades coupled to a hub, the motor comprises a stationary part and arotating part, and the rotor is attached to the rotating part of themotor.
 11. The aircraft of claim 1, wherein a first half of all liftrotors of the aircraft rotate in a first direction, and a second half ofall lift rotors rotate in a second direction opposite to the firstdirection.
 12. A method for controlling an aircraft to transition fromvertical flight to forward flight, the method comprising: providing anaircraft comprising: a fuselage; a wing coupled to the fuselage; a firstplurality of lift rotors located aft of a center of gravity of theaircraft, the first plurality of lift rotors coupled to the fuselage, atleast one of the first plurality of lift rotors having a first cant andat least one of the first plurality of lift rotors having a second cant,the second cant having an angle different from the first cant; a secondplurality of lift rotors located forward of the center of gravity, thesecond plurality of lift rotors coupled to the fuselage, at least one ofthe second plurality of lift rotors having a third cant and at least oneof the second plurality of lift rotors having a fourth cant, the fourthcant having an angle different from the third cant, wherein the fourthcant has an angle different from the first cant and the second cant,wherein the first plurality of lift rotors and the second plurality oflift rotors are coupled to the fuselage via one or more rotor booms; apropeller coupled to the fuselage for providing forward thrust; and aflight computer, coupled to the fuselage, and configured toindependently control an amount of thrust provided by each of the firstplurality of lift rotors and each of the second plurality of lift rotorsaccording to a difference between a current orientation of the aircraftand a desired orientation of the aircraft; activating the firstplurality of lift rotors and the second plurality of lift rotors;determining that the aircraft has reached a predetermined altitude;activating a forward propeller based on reaching the predeterminationaltitude; comparing a speed of the aircraft to a stall speed of theaircraft; and deactivating the plurality of lift rotors when the speedof the aircraft is greater than the stall speed of the aircraft.
 13. Themethod of claim 12, wherein equal power is applied to each of theplurality of lift rotors during the vertical lift off.
 14. The method ofclaim 12, wherein a power applied to a first lift rotor among theplurality of lift rotors is different than the power applied to a secondlift rotor during the vertical lift off.
 15. The method of claim 12,further comprising: when the speed of the aircraft is less than or equalto the stall speed of the aircraft: determining an amount of requiredlift; and adjusting power to the plurality of lift rotors to achieve theamount of required lift.
 16. The method of claim 12, wherein a powerapplied to a first lift rotor among the plurality of lift rotors isdifferent than the power applied to a second lift rotor during thevertical lift off.
 17. The method of claim 12, further comprising: afterdeactivating the plurality of lift rotors: determining a transition fromforward flight to vertical flight is required; reducing trust of theforward propeller; activating the plurality of lift rotors for thevertical flight; and stopping the forward propeller.
 18. The method ofclaim 17, wherein the transition from the forward flight to the verticalflight is determined based on a predetermined flight trajectory.